SQL Interview Guide
A complete SQL interview guide: how SQL interviews work, a study plan, and 30+ real questions with SQL answers, from joins and GROUP BY to window functions and puzzles.
Explore the latest SQL tips and tutorials in our blog section. Learn SQL programming, database management, and query optimization.
A complete SQL interview guide: how SQL interviews work, a study plan, and 30+ real questions with SQL answers, from joins and GROUP BY to window functions and puzzles.
A complete SQL window functions guide: OVER, PARTITION BY, frames, ROW_NUMBER, RANK, LAG and LEAD, and running totals, with runnable examples and their results.
The complete SQL joins guide: INNER, LEFT, RIGHT, FULL, CROSS and SELF joins, semi and anti-joins, ON vs WHERE, and join performance, with examples and result tables.
A categorized SQL functions list, aggregate, string, numeric, date/time, conditional and conversion functions, each with syntax, an example and the result.
A complete SQL syntax guide: statement structure, clause and logical processing order, identifiers, literals, operators, NULL logic, and cross-database differences explained.
A complete SQL tutorial for beginners: SELECT, WHERE, JOINs, GROUP BY, INSERT/UPDATE/DELETE and CREATE TABLE, taught step by step with runnable examples and their results.
Ten common database design mistakes, from missing keys and wrong data types to CSV-in-a-column and EAV abuse, each with the consequence and the fix, shown in DDL.
How to build enterprise databases with SQL: data modeling, constraints, indexing, partitioning, security, and high availability, with DDL examples and a design checklist.
SQL code review best practices: catch correctness, injection, and performance issues with bad-versus-good examples, a review checklist, and a reviewer rubric.
A phase-by-phase database migration checklist: assess, choose a strategy, convert the schema, move and validate data, cut over cleanly, and keep a tested rollback plan.